1. Technical Field
The present disclosure relates to a transmission apparatus, a reception apparatus, a transmission method, and a reception method.
2. Description of the Related Art
Analog Signal Transmission
In analog signal transmission, it is allowed at a receiving end to demodulate a received signal without using a reference signal or the like, and a reception apparatus is allowed to be configured in a simple form. Thus the analog signal transmission has been conventionally used in radio transmission and the like. Examples of analog signals include an amplitude modulation (AM) signal which is obtained by modulating a signal to be transmitted to an amplitude component of a carrier wave.
Because the analog signal transmission can be realized with a simple configuration and for other reasons, the analog signal transmission is attracting attention as one of techniques used in future wireless communication (see, for example, Thanh Hai Vo et al. “SSB transmission using analog SC-FDE”, IEICE Technical Report RCS 2013-60, June, 2013). For example, in the analog signal transmission, it is allowed to demodulate a received signal without using a reference signal or the like, the analog signal transmission is expected to be useful for broadcast communication in which nonconfidential information is transmitted from one sender to a plurality of receivers.
Compared with digital signal transmission, the analog signal transmission has features described below.
First, an advantage of the analog signal transmission is that a transmission delay is small compared with the digital signal transmission. In the digital signal transmission, when analog information such as an audio signal is transmitted, it is necessary to perform a quantization process to convert the analog signal to a digital signal, and it is also necessary to perform further signal processing such as channel coding, decoding, etc. The analog signal transmission does not need such processing, and thus a delay due to such processing is suppressed.
On the other hand, a drawback is a poor transmission characteristic. In general, the analog signal transmission is used for transmission of audio signals, and thus a signal band thereof is narrow compared with the digital signal transmission. Because of the narrow signal band of the analog signal transmission, frequency nonselective fading may occur in the band, which may cause a possibility of an occurrence of a large reduction in reception level over the signal band. Such a reduction in reception level is due to an influence of fading in multipath propagation channels, and thus a reduction in reception level can occur anywhere regardless of transmission time, a transmission frequency, and a reception location. When a reduction in reception level of a received signal occurs at a receiving end, the ratio of noise power to signal power increases, and thus degradation in transmission characteristic occurs.